Band saw machines have heretofore been used as devices for cutting large work pieces made of metal, for example. Band saw blades frequently used in these band saw machines are so-called bi-metal band saw blades which use as materials high-speed tool steel or cemented carbide for blade edges and strong spring steel for body portions.
In order to achieve more efficient cutting, the following bi-metal saw blades have been put into practical use: a variable pitch saw blade including tooth tips at multiple different pitches to reduce cutting noise; a kerf-dispersing type tooth-shape saw blade configured to generate smaller chips to reduce cutting resistance by setting such different set widths that the set width for a tooth having a smaller tooth height (a distance from a reference position to a tooth tip) is set larger; a saw blade having a tooth tip shape in which the tooth tip is provided with a chip curler for improving discharging efficiency of chips; and the like.
As for cutting with the band saw machine, a chip C is generated and attached to a tooth tip when a cutting object made of metal is cut with a band saw blade BS which includes: multiple saw teeth ST having straight teeth as well as right and left set teeth; and gullet portions G provided between the saw teeth ST, as shown in FIG. 1. The attached chip C is forcibly knocked off with a wire brush provided on the band saw machine and the chip thus removed and dropped off is discharged to a dedicated box outside the band saw machine by use of a chip conveyor provided to the band saw machine.
Here, in the case of cutting a cutting object such as stainless steel which has ductility and has lower thermal conductivity than mild steel or in the case of performing high-speed cutting, the chip C generated along a rake surface of the cutting blade ST is easily attached to the rake surface due to a high friction heat on the rake surface, as shown in FIG. 1. By repeating this action, the chips are tightly attached and eventually become irremovable with the wire brush. Hence there is a problem that clogs occur inside the gullets G and adversely affect precision of a cut surface, damages on the tooth tips of the saw blade, and the like.
In addition, when a largely curled chip C as shown in FIG. 1 is discharged by use of the chip conveyor, there is a problem that the chip gets stuck to the chip conveyor, and thus cannot be discharged.
To solve the above-mentioned problems, there are disclosed band saw blades having a chip curler portion provided to a rake surface of a saw tooth. The related techniques have been disclosed in Japanese Patent Application Laid-Open No. Hei 6 (1994)-716 (Patent Document 1), Japanese Patent Application Laid-Open No. 2005-349512 (Patent Document 2), Japanese Patent No. 3870158 (Patent Document 3), and Japanese Patent Application Laid-Open No. 2003-334721 (Patent Document 4).
FIG. 2(a) shows an embodiment disclosed in FIG. 3 of Patent Document 1. This has been proposed to generate effectively curled chips, and is a device of a typical saw blade having a chip curler provided to a tooth tip.
When high-speed cutting is carried out by using the saw blade thus configured, the chips are made compact and an effect against clogging is exerted. Moreover, the chips can be discharged without any problem by using the chip conveyor provided to the band saw machine.
Based on the description of the specification, tooth angles of this saw blade have general design values: a rake angle of 9°; and a tooth angle of 48.5°. Meanwhile, the chip curler has a shape protruding from the tooth tip in a saw blade cutting traveling direction (rightward in FIG. 2(a)) by an amount of 0.15 to 1.5 mm. Accordingly, when a comparison is made as shown in FIG. 2(b) with reference to dimensions of this saw blade, it is understood that a curvature radius of a curved portion at a tooth bottom is apparently smaller than that of a saw blade designed with the same tooth angle but without the chip curler (a comparison between R2.0 and R2.4).
In FIG. 2(b), a distance between the tooth tips (a pitch) is 8.17 mm. This dimension is within pitches from 6.35 mm to 8.47 mm of a variable pitch ¾ (a combination of multiple pitches indicating the number of teeth per inch, which includes the pitches corresponding to 4 teeth at maximum and 3 teeth at minimum) most frequently used in band saw blades. If the pitch becomes even smaller, the curvature radius of the curved portion at the tooth bottom, i.e., a curvature radius of a backside of a gullet bottom portion becomes smaller.
Cutting with a band saw machine is carried out as follows. Specifically, as shown in FIG. 6, a band saw blade 10 under a tensile force (tensional force) applied by two wheels 13 and 15 is twisted upward at a central portion by saw blade guides 17 and 19 to direct tooth tips toward a work. Then the band saw blade 10 is rotated with rotation of the driving wheel 13 while a housing of the band saw machine is lifted down at the same time.
Here, the band saw blade 10 repeatedly receives: tensile stress due to the tensile force by the two wheels; bending stress due to the twisting actions by the wheels and the saw blade guides 17 and 19; and cutting resistance from the work.
Accordingly, the band saw blade around the tooth bottoms receives the concentrated stresses, whereby a body portion may cause breakage (early body breakage) even though the tooth tips are still capable of cutting. Moreover, in recent years, speeding-up of a cutting process has increased the tensile forces on the band saw machine and brings about a cutting environment where the breakage is more likely to occur. As a countermeasure for these problems, a method of relaxing the concentrated stress by increasing the curvature radius of the curved portion at the tooth bottom is adopted.
However, the saw blade in the shape with the chip curler provided to the rake surface has the smaller curvature radius of the curved portion at the tooth bottom than the conventional band saw blade having no chip curler as described above in FIG. 2(b), and therefore easily causes the early breakage.
FIG. 3 shows an embodiment disclosed in Patent Document 2.
This is a proposal to discharge chips smoothly without causing chipping while providing no reinforcing portion to a tooth tip.
According to this proposal, a rake surface is provided with a shape like a chip curler. Based on the description of the specification, this proposal aims to prevent adhesion of a chip by reducing contact between the chip and the rake surface and thereby to smooth discharge of the chip by use of the wire brush, but does not provide a proposal to make the chip smaller and compact. In high-speed cutting with this configuration, the gullet is filled and clogged with a chip having a large diameter corresponding to the size of the gullet whereby the cut surface becomes coarse. Moreover, the problem of incapability of discharge by using the chip conveyor provided to the band saw machine is not solved.
In addition, as shown in FIG. 2(b), this band saw blade also has a smaller curvature radius of the curved portion at the tooth bottom than the conventional band saw blade having no chip curler, and therefore easily causes the early breakage.
FIG. 4 shows an embodiment disclosed in Patent Document 3.
This is a proposal to enhance strength against chipping by increasing a length dimension of a bi-metal boundary portion, i.e., a portion where the blade and the body are welded together.
Although a portion of the rake surface is formed into a shape like a chip curler, no description for making chips compact is found in the description of the specification and the effect thereof is therefore unknown.
In addition, this band saw blade also has a smaller curvature radius of the curved portion at the tooth bottom than the conventional saw blade, and therefore easily causes the early breakage.
FIG. 5 shows an embodiment disclosed in Patent Document 4.
This proposed embodiment includes a first rake surface and a second rake surface. In order to prevent a chip along the first rake surface from coming into contact with the second rake surface, the second rake surface extends from a junction portion with the first rake surface in an opposite direction to a cutting traveling direction and connects to a tooth bottom. This configuration makes the chip less likely to adhere to the tooth bottom and easily removable with the wire brush or the like.
According to this configuration, the rake surfaces include no shape like a chip curler. The description of the specification includes no description for making chips compact.
Moreover, this saw blade also lacks the description for increasing a curvature radius of the curved portion at the tooth bottom connecting the rake surface to the tooth bottom.
The band saw blade with a shape having the chip curler provided to the rake surface includes a protrusion in a direction of the rake surface, unlike the conventional band saw blade, owing to the characteristic shape thereof (see FIG. 2(b)). Accordingly, the curvature radius of the curved portion at the tooth bottom is small and the early breakage easily occurs. However, in order to avoid concentration of the stress on the curved portion at the tooth bottom on the rake surface of the tooth tip for preventing the early body breakage, it is necessary to increase the curvature radii of the curved portions at the tooth bottoms on all the rake surfaces of the tooth tips provided with the chip curlers.